Wristwatches are already known wherein the glass is provided with touch keys for electronically starting a time function or a non-time related function. These touch keys are structured by transparent conductive material evaporation techniques on the inner surface of the glass which is opposite the watch dial. These keys are for example capacitive keys. In other words, when the user applies his finger on the watch glass, there is a variation in the capacitance of the capacitor formed between the finger and the glass, which is interpreted by the watch electronics as a control signal for the function associated with the touch key that has been activated.
Techniques for structuring transparent touch keys on a watch glass are now well understood. They remain, however, long and thus expensive to implement. Another drawback of the touch keys briefly described above is that they cannot be activated when the watch is in water.
It is an object of the present invention to overcome the aforementioned problems, in addition to others, by proposing a new type of device for starting an electronic function in a portable object such as a wristwatch, which is much simpler to install and therefore less expensive.